In general, two important aspects of end-to end signal transmission performance of a device under test (DUT) or a communication channel are a shape of an impulse response of the DUT or the communication channel and a propagation delay of the DUT or the communication channel. These two important aspects are used in transmittance measurements that are further utilized in applications for characterizing multipath propagation effects, dispersion effects in optical cables, impedance spectroscopy of large objects and propagation delay skew. In order to utilize the transmittance measurements in various applications, the propagation delay in the DUT needs to be measured initially.
There are several techniques known in the art for measuring the propagation delay of the DUT and the transmittance. One such measurement technique employs a vector network analyzer (VNA) as a measurement unit in which two ends of the DUT are connected to the same measurement unit. The measurement unit sends a test signal from a transmitter port of the measurement unit to the DUT and receives a signal from the DUT at a receiver port of the measurement unit. The measurement unit, then, calculates transmission properties of the DUT by measuring a S-parameter for the transmittance at a plurality of frequencies.
Further, in another measurement technique, the propagation delay in the DUT is measured by performing reflectometry using either a time domain reflectometer or a frequency domain reflectometer. In a reflectometry based measurement unit, a first end of the DUT is connected to a test port of the measurement unit and a second end of the DUT is connected to a reflective termination. For measuring the propagation delay in the DUT, a source of the measurement unit generates an excitation signal and provides the excitation signal to a directional coupler. The directional coupler further transmits the excitation signal to the DUT through the test port. Thereafter, a receiver of the measurement unit receives a signal reflected from the reflective termination. Thereafter, a receiver of the measurement unit calculates the propagation delay between the excitation signal and the reflected signal.
However, the measurement techniques using the VNA are not capable of performing a dual-ended phase-sensitive testing for a large DUT such as a long cable, as a length of the DUT makes it impossible to connect two ends of the DUT to the same measurement unit. Further, the measurement techniques using the reflectometer do not provide a required accuracy in a measurement of the propagation delay. Also, the reflectometer based measurement techniques are not suitable for measurements for DUTs having multiple ports, an example of such measurement being Far End Cross-talk (FEXT) for multi-conductor cables. Further, the existing techniques are not suitable for vector S-parameter measurement of FEXT.
Therefore, in light of the above, there is a need for a method and system for performing a dual-ended propagation delay measurement and transmittance measurement without requiring a common phase reference between two independent measurement units, wherein the two independent measurement units may not have any physical or conductive electrical connection between them.
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